WASHINGTON—The Obama administration and its European allies—surprised and encouraged by
Hassan Rohani's
election as Iran's next president—intend to aggressively push to resume negotiations with Tehran on its nuclear program by August to test his new government's positions, U.S. and European diplomats say.

Mr. Rohani, 64 years old and a centrist figure on the Iranian political stage, on Saturday trounced a host of more conservative candidates to succeed
Mahmoud Ahmadinejad
,
a president who famously staked out confrontational positions with the West. Mr. Rohani campaigned on ending Iran's international isolation and reinvigorating its economy.

ENLARGE

Supporters of moderate cleric Hassan Rohani celebrate his victory in Iran's presidential election along a street in Tehran on June 16.
Reuters

The diplomacy between Iran and global powers aimed at curbing Tehran's nuclear work has been frozen since April. American and European officials said Sunday they believed Iran's overall nuclear policy will remain tightly controlled by Supreme Leader Ayatollah
Ali Khamenei.
The 73-year-old cleric has refused to authorize any concessions during the past four years of international talks that have involved Iran and the five permanent members of the United Nations Security Council, plus Germany.

Iran Election Watch

Learn more about the structure of the Iranian government and the candidates who ran for president.

Washington and Brussels are eager to quickly test whether Mr. Rohani's unexpected victory could pressure Mr. Khamenei into softening his position on the nuclear issue or scaling back Tehran's broader rift with the West, these officials said.

Iran, along with Russia, is an important backer of Syrian President
Bashar al-Assad.
The Syrian government is consumed by a broadening civil war with rebel groups that are armed and financed by the U.S. and its European and Arab allies.

Many Iranian voters, as well as many of the presidential candidates, sharply criticized Tehran's handling of the nuclear issue during the campaign. They also blamed the government for a worsening economic crisis driven in part by mounting U.S. and European sanctions on Iran that are aimed at forcing Tehran into making concessions on its nuclear program.

More Coverage

During a televised debate a week before Friday's vote, candidates ganged up on
Saeed Jalili
—who, in addition to being a candidate, is also Iran's current chief nuclear negotiator—slamming his negotiating skills. Mr. Rohani said at the debate it was time the nuclear issue went into the hands of someone with "an understanding of diplomacy" and "the world."

U.S. and European officials said Mr. Rohani's election offers Mr. Khamenei an opening to shift Tehran's diplomatic course, though they remained skeptical that he would do so. "I think the question for us now is, if [Mr. Rohani] is interested in, as he has said in his campaign events, mending Iran's relations with the rest of the world, there's an opportunity to do that," White House Chief of Staff Denis McDonough said Sunday on CBS's Face The Nation. "If he lives up to his obligations under the U.N. Security Council resolution to come clean on this illicit nuclear program, he will find a partner in us, and there will be an opportunity for that."

Tehran denies it is seeking atomic weapons and says it is developing nuclear technologies only for energy and medicine.

U.S. officials said the Obama administration was genuinely stunned by Mr. Rohani's electoral victory.

Mr. Jalili, the current Iranian nuclear negotiator, had been seen as a favorite of the Supreme Leader. Two other candidates who expressed the most willingness to challenge the government's policies, including former President Ali Akbar Hashemi Rafsanjani, were barred by an official government body from participating in the vote.

Mr. Rohani's moderate voice on the international stage, particularly in comparison to Mr. Ahmadinejad, could serve to divide the international community on the need to maintain or intensify economic sanctions on Iran, even if the country doesn't suspend its nuclear work. "Rohani's election may mean that Khamenei realizes the extent of Iran's crisis and is willing to let Rohani pave a way forward," said Alireza Nader, a Washington-based Iran analyst at Rand Corp.

Mr. Rohani's election poses a challenge for Israel, according to analysts, to keep persuading the international community of increasing pressure on Iran. Prime Minister Benjamin Netanyahu said Sunday to the Israeli cabinet, "The international community must not become caught up in wishful thinking,'' adding that the Iranian regime considers Israel a "Zionist satan."

In 2003, Mr. Rohani was a member of the National Security Council when 127 Iranian parliamentarians signed an open letter to Mr. Khamenei urging him to freeze enrichment of uranium to ward off the threat of war. President George W. Bush had recently labeled Iran as part of an "axis of evil."

Mr. Khamenei didn't answer the letter, and conservative media began slamming the signatories. In the background, Mr. Rohani began lobbying with Mr. Khamenei and a circle of his advisers. Eventually, he persuaded Mr. Khamenei to sign off on a document called the Tehran Declaration, where Iran agreed to cooperate with IAEA, the U.N.'s nuclear watchdog, and freeze enrichment for the duration of the negotiations.

"Rohani took the middle ground," said Ali Akbar Mousavi Khoeini one of the reformist parliamentarians who had signed the original letter, "and managed to execute our demand. He didn't do it our way, he went about it very quietly and politically." Mr. Mousvi Khoeini, who now lives in the U.S., added that Mr. Rohani benefits from having forged strong connections with both conservatives and reformists.

Mr. Rohani's past positions on Iran's nuclear program signal both opportunities and warning signs for the West, according to U.S. and European officials who have worked on the nuclear issue.

The Islamic cleric and government insider served as Tehran's chief nuclear negotiator from 2003 to 2005 and currently heads the Supreme National Security Council, the Iranian government's top foreign policy-making body.

In 2004, Mr. Rohani agreed with European powers to temporarily freeze development of nuclear facilities in exchange for economic incentives. The deal was viewed as a breakthrough at the time and raised hopes Tehran was seeking to normalize relations with Europe and the U.S.

Mr. Ahmadinejad, however, later ended the freeze. And Mr. Rohani has since suggested that the agreement was a negotiating ploy to lessen international pressure on Iran.

"While we were talking with the Europeans in Tehran, we were installing equipment in parts of the facility in Isfahan," the president-elect said in a speech in Tehran, referring to a key nuclear-fuel production site. "In fact, by creating a calm environment, we were able to complete the work in Isfahan."

While the core of Iran's nuclear policy, which is centered on the right to enrich uranium for peaceful purposes, might not change, it is likely that Iran's negotiating strategy will shift, analysts say.

Mr. Rohani already alluded to a possible change in dealing with the world in his victory speech Sunday. However, he made it contingent that the West should also change its tone.

"There is a new opportunity in the international sphere for those [countries] who respect people's rule and freedom of speech to speak to Iran in a respectable and accepting tone. They will hear back a positive answer," said Mr. Rohani.

This copy is for your personal, non-commercial use only. Distribution and use of this material are governed by our Subscriber Agreement and by copyright law. For non-personal use or to order multiple copies, please contact Dow Jones Reprints at 1-800-843-0008 or visit www.djreprints.com.